Marco R. Brendel, Frank M. Schurr and Christine S. Sheppard
Institute of Landscape and Plant Ecology, University of Hohenheim, 70593 Stuttgart, Germany
When introduced into a new area, alien species are exposed to novel climatic conditions, which can have negative effects on their establishment, fitness, and population growth. In this regard, differences in climate between the native and the introduced range (climatic dissimilarity) act as a barrier to invasion. With the time since introduction of an alien species into a new area (residence time), its establishment rate and invasiveness are predicted to increase. This leads to the assumption that alien species possibly cope better with local climatic conditions the longer they are present in a new area, thereby overcoming initial climatic barriers (e.g. through rapid evolutionary changes). However, in studies on invasion success, population dynamics in relation to species’ residence times have been greatly neglected so far. To address the question if a negative effect of climatic dissimilarity on invader performance weakens with residence time, we performed a common garden experiment based on a species-for-time approach. Particularly, we compiled a set of 46 annual Asteraceae species (with 115 populations) along an alien-native continuum, thereby covering a wide range of residence times in Germany (7 to 12,000 years). We investigated their population dynamics (initiated at low density) in monoculture mesocosms (preventing seed immigration and emigration) over two years. We tested for the effect of climatic dissimilarity (measured as temperature difference between the species’ global distribution and the local conditions) in relation to residence time on five different demographic performance measures. In the first year, temperature difference had a strongly negative effect on the finite rate of increase. Intriguingly, this effect weakened with the residence time of Asteraceae species in Germany. For the demographic components, establishment rate and fecundity, we found similar effects. Population growth and size in the second year showed no clear response to temperature difference depending on residence time but seemed to be driven by density dependence instead. Our results revealed that initially, climatic dissimilarity acts as a barrier to invasion in a new area, however, its effect decreases over eco-evolutionary timescales. This will provide a better understanding of the mechanisms behind constraints on population growth and spread of invaders.